Abstract. Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high nutrient low chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) was applied. Our results indicated that organic ligands in surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea-ice. Organic ligands in deeper shelf water are supplied via resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([L_t]) were between 1.2 nM eq. Fe and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentration (excess ligand concentration, [L'] = 0.8–5.0 nM eq. Fe). The [L'] made up to 80 % of [L_t], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe (α_Fe'L; the product of [L'] and conditional binding strength of ligands, K_Fe'L^cond). Since Fe is also supplied by shelf sediments and glacial discharge, the high complexation capacity over the shelf can keep Fe dissolved and available for local primary productivity later in the season, upon sea ice melting.

中文翻译：

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南极半岛西部地表水中铁结合有机配体的来源

摘要。有机配体是决定南大洋高营养低叶绿素（HNLC）地区溶解铁（DFe）可用性的关键因素。在这项研究中，沿着南极半岛西部的自然梯度，从冰覆盖的架子到开阔的海洋，研究了铁的有机形态。采用电化学方法，竞争性配体交换-吸附阴极溶出伏安法（CLE-AdCSV）。我们的结果表明，架子上地表水中的有机配体与冰藻渗出物有关，可能与海冰融化有关。较深的架子水中的有机配体通过斜坡或架子沉积物的重悬而提供。在更远的海上，有机配体最有可能与开放海水中浮游植物大花的发展有关。在架子上，_t ]）在1.2 nM当量之间。Fe和6.4 nM当量 铁 离岸的有机配体的范围在1.0和3.0nM当量之间。铁 南极绕极流（SB ACC）的南边界将架子上的有机配体与离岸水华相关的配体隔开。总体而言，有机配体浓度始终超过DFe浓度（过量配体浓度，[L'] = 0.8–5.0 nM当量铁）。[L']占[L _t ]的80％，这表明可以通过有机络合将任何额外的Fe输入稳定在溶解形式中。架子上较稠密的改性圆极深水（mCDW）显示出最高的Fe（_αFe'L络合能力； [L']与配体的条件结合强度的_乘积K _Fe'L ^cond）。由于铁还由架子沉积物和冰川排出物供应，因此架子上的高络合能力可以使铁保持溶解状态，并在海冰融化后的季节后期可用于当地的初级生产力。